Italian railway signalling

The Italian railway signals currently in use have evolved from the ones used at the dawn of the rail era. In Italy, trains drive on the left on double track lines, probably because the first state to set up railways (Britain) chose the left. This led to the need to place signs on the left of the track (except in cases of physical impossibility to mount them conventionally, in which case they are on the right).

The Italian State Railways network (Ferrovie dello Stato Italiane) uses both light and mechanical (or semaphore) signals. On high-speed lines, trackside signals are replaced by cab signalling and only marker signs for section ends or service areas are installed by the track.

Signals are divided into home (1a categoria) and distant (avviso) categories.

In some stations, usually larger ones, signals can control safety and/or departure, in which case they are called 'multiple signals’; separate signals will have a plate bearing the inscription "INT" (interiore) on the signal closer to the station (possibly followed by a number in case there is more than one internal signal), and "EST" (esteriore) on the farther signal. The signals can also indicate the beginning of a block. In case of multiple signaling starting, the starting signal also functions as a block signal.

Distant signals are placed ahead of home signals at a distance of 800, 1000 or 1200 meters to allow braking from the maximum speed allowed (except on high-speed lines, which have longer distances). They give the operator a warning in order to be able to observe the instructions of the following home signal.

If a distant signal is close to a following home signal (i.e. when the distance between two consecutive home signals is equal to or lower than 1,500 meters, or a maximum of 2,000 meters in special cases), the two signals are combined into a single signal with a home function as well as a distant signal for the home signal immediately following. These are called coupled distant signals (avviso accopiato).

Home semaphore signals are composed of a rectangular arm red with a white band. Distant semaphore signals preceding a home semaphore have a yellow arm with white stripe and a fish tail shaped ends, and show at night show a light green for 'green' or a yellow light for 'danger'.

Distant semaphore signals use a red rectangular arm with a white band, in which is a black '2'. They can only be the semaphore type. At night, distant signals show a red light if the arm is horizontal or a green light if it is down. Unlike home signals they are not placed immediately before the point to be protected, but rather at a distance sufficient distance for the train to slow down before reaching the protected point.

These signals are never preceded by a distant signal, but they are preceded by a warning yellow rhomboid signal if they are not visible from a specified minimum distance (depending on the line's grade, 400, 600, or 800 m if the maximum line speed is not greater than 80 km/h for the "A"-class and 90 km/h for the "B"-class, or else 1000 m).

Light signals are composed of one, two or three lights in a black plate with white border. In tunnels the plate is absent. The signs are placed on their own posts or can be applied to catenary posts.

Light signals give orders to the driver through different 'aspects', comprising one or more coloured lights. The colours used are: red, yellow, and green, and they can be fixed or flashing lights, single or grouped.

Italian signals are unusual in that one lamp is used to display different colours. Most other countries do not employ moving parts in light signals. Each light in a signal is composed of a lamp and a rotating disc with different colour filters (red, yellow, green, black (light off)). Newer signals are composed of three white lamps, placed in different positions within the signal followed by a red, yellow or green color filter and a system of one or more dichroic filters which direct light of the desired color to an aspheric lens that in turn directs the beam out of the projector to the direction of the trains which the signal controls. The lamp is protected against reflections of the sun by a tubular shade.

Italian light signals consist of one to three single lamps. At least the upper lamp is always turned on. The lights can be fixed or flashing. In candlestick signals, each arm has one or two lights. At least one light of each arm is on.

The signs are usually placed to the left of the track which they control (in Italy, train circulation is normally on the left-side track), and their plate is circular. In some cases they can be placed on the right (e.g. station platforms, double-track lines with the safety equipment is on the left of the track rather than on the right). In this case the plate is square, and can include a white arrow light placed over the signal and pointed towards the track that comes on only when the signal is green or can be passed. Home, distant and combined home and distant signals are of similar appearance, except that distant signals are distinguished by a black and white hooped mast. Combined signals can be equipped with a display below the bottom light called 'Rappel' that serves to indicate speed limits with immediate effect.

Home signals have one two or three lights arranged one above the other. They can indicate halt or line clear aspects or give speed signals. The speed limit (30, 60 or 100 km/h) is given by the preceding distant signal. If the signal has a 'Rappel' plate illuminated, then the speed limit starts at the home signal.

Station protection signals and station departure signals can be multiple or '’candelabra’'; they can comprise several lights on a number of separate arms for support.

Multiple home signal signals consist of several primary signals grouped together. The order of the signals from left to right, is the same as the routes or groups of routes they control. The uppermost light commands a route without speed restrictions, those placed below control routes with a speed limit after the next set of points depending on the presence of a warning aspect or a reminder signal placed under the signal. In the absence of any indication, the maximum speed is 30 km/h.

Where the lights are all at the same level they will be regarded as lower level and imply speed limits on all routes they controlled.

Candlestick at clear signal to the middle route, without speed restriction

Coupled distant signals combine home aspects controlling drivers actions at the signal and distant aspects warning of the aspects of the following home signals. There are no separate ‘home’ and ‘distant’ lights, the various aspects indicate both home and distant instructions together.

In general, to signal a speed restriction as a distant aspect (i.e. when the next signal is not at 'line clear' then the top light shows yellow. To signal a speed restriction as a home signal then the 'Rappel' display is activated with no (= 30 km/h), one (= 60 km/h) or two (= 100 km/h) bars.

Line blocked and abnormally close (less than 600/900m but not less than 350m) or track is somehow obstructed. In the latter case, the next signal will show the aspect "red and double yellow."

Unlike other respects, this aspect is always preceded by a yellow distant signal which 'requires' a speed reduction to 30 km/h!

Example of left and right placed signals

On the left, the signal controls the track to the left of the signal. This is indicated by the white arrow at the top and the square plates. The yellow 'INT' plate below the lights indicates that the protected sections are at the entry to a station. On the right, the signal controls the track to its right (no arrow, round plates). The signal is showing red on yellow, meaning the next signal is set to stop. The 'rappel' plate is showing two horizontal bars meaning the driver should slow to 100 km/h immediately.